A vehicle typically includes a heat exchange assembly positioned at a front of an engine to cool the engine. The heat exchange assembly generally comprises a fan and a radiator. The fan is disposed on a shroud and the shroud is connected to the radiator. As shown in FIGS. 1A and 1B, the shroud S includes a plurality of ventilation apertures V and each ventilation aperture V includes a flap P. As shown in FIG. 1B, when the vehicle is traveling in a high speed, airflow F will go through the radiator R under the fan's suction, push the flap P open and then flow to the back of the fan. When the vehicle is idling, the flap P cannot be pushed open due to a small airflow F. Thus, the flap P prevents airflow to recirculate from the back of the fan to a clearance between the shroud S and the radiator R.
As the flap P is a single part independent from the shroud S, a cost of the shroud installed with the flap is high. However, if the flap is removed, the ventilation aperture V is open completely. When the vehicle is idling, airflow F will flow back from the backside of the fan to the clearance between the shroud S and radiator R as shown by arrow A in FIG. 1B and thus reducing the heat exchange efficiency.